The present invention relates to a transparent, vinylidene fluoride resin-based shaped product exhibiting an effect of shielding off ultraviolet rays.
Many organic polymers such as polyethylene, polypropylene, polyvinyl chloride, saturated and unsaturated polyesters, and polycarbonate gradually deteriorate on exposure to sunlight, and certain polymers exhibit an undesirable discoloration. This phenomenon results from the fact that these polymers are very sensitive to the ultraviolet rays in sunlight, particularly light at wavelengths of from 290 to 400 millimicrons. In contrast, vinylidene fluoride resins, particularly polyvinylidene fluoride have a very high resistance to ultraviolet rays. The vinylidene fluoride resins are characterized by the fact that no deterioration takes place therein even when the resins are exposed to sunlight for a long period of time.
However, when some substance is packaged with films of a vinylidene fluoride resin, the substance cannot be protected from light deterioration. When a substrate is coated with a film of a vinylidene fluoride resin, there is also hardly any protection of the substrate. This is because, at the same time that a vinylidene fluoride resin has ultraviolet ray resistance, it also has an extremely high transmittance of ultraviolet rays.
Generally, it is well known that the light deterioration of a substance packaged or coated with polymers having large transmittance of ultraviolet rays can be decreased by mixing an ultraviolet absorber into the polymers. However, when an ultraviolet absorber disclosed in Japanese Patent Pub. NO. 11224/1962, for example, is added to polyvinylidene fluoride, it is difficult to completely mix the absorber with polyvinyl fluoride. Similarly, other general commercially available ultraviolet absorbers cannot be completely admixed with polyvinylidene fluoride.
Because polyvinylidene fluoride has a high crystallinity, the processing temperature is relatively high and the compatibility with most compounds is poor. When a general-type ultraviolet absorber is added to polyvinylidene fluoride, the ultraviolet absorber having a high vapor pressure is liable to vaporize off during the processing. Even if the absorber can be made to remain in the polyvinylidene fluoride by adding a large amount of the absorber, the absorber tends to become isolated gradually from polyvinylidene fluoride to bleed over or leach out of the surface of the polyvinylidene fluoride.
Accordingly, the property of shielding off ultraviolet rays of the shaped product in which the ultraviolet absorber is admixed into polyvinylidene fluoride gradually decreases with the elapse of time. When an absorber having poor compatability is mixed with polyvinylidene fluoride, the transparency of polyvinylidene fluoride is decreased.
In order to solve such problems, Japanese Patent Pub. No. 48897/1977 has proposed a polyvinylidene fluoride composition in which a copolymer of 2-hydroxy-4-(4-methacryloxy-2-hydroxypropoxy)benzophenone and methyl methacrylate or ethyl methacrylate is used as an ultraviolet absorber.
However, this composition is slightly unsatisfactory in transparency. Further, the compatibility of this ultraviolet absorber with polyvinylidene fluoride is still insufficient, and therefore a large amount of the ultraviolet absorber cannot be mixed into polyvinylidene fluoride. When the thickness of a thin film formed from such composition is, for example, several microns it is impossible to completely shield off ultraviolet rays by means of such a thin film. Because polyvinylidene fluoride is an expensive resin, it is desired that the thickness of the film be thin in order that it can be widely used in various industries.